Further study on NAA in characterizations of reference materials

Characterizations of three major parameters of Certified Reference Materials (CRMs) concentration values of multielements, homogeneities of multielements, and stabilities of the materials, were further studied by NAA. In the determinations of multielements in RMs, both relative and K0 (and its extension) standardizations were used in an effort to detect hidden systematic errors and expand the number of determinable elements. In the evaluations of multielemental homogeneities, double sampling constants as well as Ingamells' Ks and F-test were used to establish semi-quantitative expressions of sampling uncertainty vs. size and number of subsamples for given elements in given materials. For the investigation of the stabilities of certified values, K0 NAA is to be used in follow-up analyses to test variations of certified values and provide updated and/or newly determined data. The final goal is to make NAA a definitive method for multi-trace element certification, a reliable method for homogeneity characterization, and reproducible method for stability test. Examples are given to show preliminary results on the above aspects. (author) 32 refs.; 1 fig.; 8 tabs